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1/22/2020 12:12:56 PM
Posted: 9/15/2009 6:04:58 PM EST
[Last Edit: 9/15/2009 6:05:52 PM EST by blood_donor]
Hi,

I am a relative newbie to "real cameras". I am running an E-520 with the 14-54 v2 lens.

I took some photos on a camping trip, and when I got home, I was sorely disappointed. Quite a few were not focused where i thought they would be. I was shooting mostly in Aperture priority mode, typically in the 20-35mm part of the zoom range, sometimes say f/5 and sometimes f/9.

Typically what I would do is point at my subject (for example, my 4 year old daughter's face), half-press the shutter button. I would see the center focus lamp light up. Then I would move the camera to compose the photo, and press the button the rest of the way.

Sometimes this worked out fine, but sometimes, the camera would focus several feet in front or behind where I thought I would get.

I doubt it is my camera, so I am thinking my basic technique must be lacking.

For example, am I shooting with too much aperture? If I rotate the camera too much, the focal plane may swing out past my subject, right?

Do I need to turn off the left and right focus points, and only use the central one?

In some photos, I used a CP filter to get nicer skies (strong sunny days). Does this cause focus problems?

Example 1: Focus point was supposed to be my daughter's face, but it looks like it focused a bit behind her.


Example 2: Focus point was supposed to be the stairs near my daughter


Example 3: Focus point was supposed to be my daughter's face, but it looks like her front knee is in focus and her face is soft.
Link Posted: 9/15/2009 6:08:04 PM EST
you might consider using focus lock when you move the camera around.. it's easy to release and half press the shutter again without realizing it.

using focus lock will prevent this.


if your camera doesn't have focus lock, you can auto focus, then (if your lens has a toggle) switch the lens to manual so it stays put.

Link Posted: 9/15/2009 7:05:05 PM EST
Typically what I would do is point at my subject (for example, my 4 year old daughter's face), half-press the shutter button. I would see the center focus lamp light up. Then I would move the camera to compose the photo, and press the button the rest of the way.
Compose the shot, then focus (shutter release half way) then shoot the image

Sometimes this worked out fine, but sometimes, the camera would focus several feet in front or behind where I thought I would get.
Because when you move, it changed the distance and focus

I doubt it is my camera, so I am thinking my basic technique must be lacking.

For example, am I shooting with too much aperture? If I rotate the camera too much, the focal plane may swing out past my subject, right?
A big aperture (hole in the lens,lower number ie: f/2.8) creates a shallow depth of field. A small aperture (hole in the lens, bigger number ie: f/22) creates more depth of field. Once you get your focus issue straightened out you can experiment with creating images with different DoF. I think if you were shooting with a high aperture (f/22 for example) your images would be all blurry due to a slow shutter speed instead of one spot in focus and the rest blurred. It looks to me like your "four point" focus system is jacking you up locking on to a place you didn't mean for it to lock on.

Do I need to turn off the left and right focus points, and only use the central one?
I 99% of the time only use one focus point for what I do. On my cameras you can change where that single focus point is. Try it, see if you like it

In some photos, I used a CP filter to get nicer skies (strong sunny days). Does this cause focus problems?
It shouldn't have any affect on focussing. Maybe if it was dark and the sensor had to "hunt" to lock on..but ordinarily, no.

Link Posted: 9/15/2009 11:03:45 PM EST
Well, I'd first of all have to say that shooting f/5 to f/9 @ 14-55mm shouldn't give you THAT shallow of a depth of field, unless you're super close to your subject.

It may be more apparent in the larger files (pixel peeping), but from your web-sized photos, I wouldn't complain about focus on any of those pictures you posted.


Having said that... there are several things that can help you with your focusing.

IMO, the most important thing is to move the focus off the shutter button, if your camera allows it. Use one button to focus, and the other to meter/snap. No reason to do all 3 on one button. This is especially helpful when you want to take several shots in a short period of time, and you don't have to refocus each time (or at least then the camera won't TRY to refocus each time).

The next big thing to consider is that (at least with Canon cameras) the red light only indicates where your camera is trying to focus at, NOT that it achieved focus properly. For Canon cameras, there is a separate indicator (green circle) that tells you that the camera ::thinks:: it has focused properly. This can easily fool you if you're not expecting it... as the camera may take time to finish focusing after it has indicated where it is trying to focus.

To assist in focusing (this is much more important in low light... probably wasn't an issue in your daylight photos), always remember that cameras determine focus based on contrast. Aiming the focus point at something with good contrast, for example where the white of someone's eye meets the iris/eyelid, will help the camera focus much much better. If you don't believe me... try to aim your focus point at a clear blue sky and see how well it does. Also remember that the red indicators won't cover the entire area that the camera is looking for contrast... in fact the indicators may be off center. This can sometimes lead to a different object being focused on, even though you point your red dot right on what you want focused.

When the camera is looking for contrast, (once again, at least with Canon cameras) the shape of the focus point indicator will help you determine which type of contrast the camera is looking for... horizontal or vertical. Try using your outside focal points (which are shaped in a rectangle) to focus on a contrasty object that has dark/light contrast running vertically... then try the same focal point & object with the camera turned 90 degrees (doing this in low light helps). One way or the other will focus better/faster.

The focus/recompose shuffle can lead to shifting the plane of focus... but at those apertures and focal lengths, I doubt this was much of a big problem. I do most of my focusing with the center focus point, even at very large apertures (f/1.2)... but I have to be careful with how much I change things, or else manually tweak the focus afterward.

One last thing that probably won't help in your scenario, but since I've typed this much, I might as well finish up... Canon cameras (and I would assume other brands, but no idea if that assumption is right or not) have a "high precision" center focus point. This is ONLY activated when you use lenses that meet or exceed the aperture requirement for the particular body you use. In the 1 series camera it is F/5.6 (actually the 1 series cameras have more than 1 HPFP), and I believe every other Canon body that has this function needs an f/4 or faster lens. What this does is uses both the vertical and horizontal contrast to focus with... and thus the reason I use the center point to AF with almost all the time.

And now I've typed all I can think of off the top of my head about getting better focus. I'm sure I've missed a good deal... but it's a good start.
Link Posted: 9/16/2009 7:38:25 AM EST
[Last Edit: 9/16/2009 7:40:09 AM EST by beavo451]
Do you have a thorough understanding of how your particular AF system works? From the photos you have posted, the focus is on the closest high contrast object.

Pic 1: The statue with the ball and the curved bricks on the ground
Pic 2: The tree on the far left
Pic 3: Her left knee

Focus/recompose technique would not result in such dramatic shifts. Are sure you don't have the camera to focus on the closest subject? (I know Nikon and Canon have this feature)

Originally Posted By purple85gt:


Sometimes this worked out fine, but sometimes, the camera would focus several feet in front or behind where I thought I would get.
Because when you move, it changed the distance and focus


At the distance, aperture, and focal lengths he is shooting at, the focal plane shift should not matter.


In some photos, I used a CP filter to get nicer skies (strong sunny days). Does this cause focus problems?
It shouldn't have any affect on focussing. Maybe if it was dark and the sensor had to "hunt" to lock on..but ordinarily, no.



YES it does matter what kind of polarizer you use. I'm assuming that by "CP", you mean Circular Polarizer. If that is the case, then yes you are using the correct polarizer. Linear polarizers will mess with a camera's AF systems.

Link Posted: 9/16/2009 5:44:59 PM EST
I usually switch the auto focus to only the center point unless I'm doing landscape shots.
Link Posted: 9/18/2009 4:02:47 PM EST
[Last Edit: 9/18/2009 4:06:22 PM EST by ColonelHurtz]
Dispense with AF until after you have mastered your manual focus.
You'll learn what "sharp" really looks like in the viewfinder TTL.
Don't even bother with an LCD display.
Learn the fundamentals of how distance to subject, focal length and aperture affect DOF and focus.

Work on your stance, a lot of what people think is poor focus is often shake or blur.
The shot on the steps has the subject in motion and your shutter is too slow to freeze it.
Notice how your wife who is even further from the focal plane appears sharper. That's because she's not moving.
Bump your ISO up or sacrifice a little DOF for shutter by opening up.

That said, my Nikon has a plethora of AF options. I default to the center zone.
I can activate and move the priority zone around the frame with the command wheel.
The pip in the viewfinder moves around to indicate the selection.
There are also several averaging functions.

Even with my PAS camera I usually center and lock the focus on the subject and then frame up.
It looks like your not holding that selection, in the shot w/ the steps, the camera has obviously selected the nearest object as the focus.
Some even have that as an AF mode.

Remember this. For people, always focus on the eyeball.
Zoom in if you have to for critical focus, then zoom out to frame.
Link Posted: 9/19/2009 11:45:47 AM EST
Originally Posted By ColonelHurtz:

Remember this. For people, always focus on the eyeball.
Zoom in if you have to for critical focus, then zoom out to frame.


Just make sure your lens(es) actually keep their focus when zooming. I am pretty sure that most Canon lenses do not do this.

On lenses for broadcast video cameras you have a backfocus adjustment (IIRC, that's what it was called...) that you can adjust to keep your focal plan the same when you zoom... but I've never seen an SLR camera lens that has this option.

Then again, if you're zooming out (especially with small aperture and/or wideangle lens), it probably won't make a big difference.
Link Posted: 9/19/2009 12:16:55 PM EST
[Last Edit: 9/19/2009 9:15:06 PM EST by ColonelHurtz]
Originally Posted By steenkybastage:
Originally Posted By ColonelHurtz:

Remember this. For people, always focus on the eyeball.
Zoom in if you have to for critical focus, then zoom out to frame.


Just make sure your lens(es) actually keep their focus when zooming. I am pretty sure that most Canon lenses do not do this.

On lenses for broadcast video cameras you have a backfocus adjustment (IIRC, that's what it was called...) that you can adjust to keep your focal plan the same when you zoom... but I've never seen an SLR camera lens that has this option.

Then again, if you're zooming out (especially with small aperture and/or wideangle lens), it probably won't make a big difference.


That's not what back focus is for.
It adjust's the rear elements relationship to the film/sensor plane.
This changes from lens to lens or when you re-mount the same lens.

The symptom is loss of focus as you zoom out when it's not adjusted correctly but it's purpose is to adjust and fix the distance in the optical train.
I'm not sure why interchangeable still camera lenses don't have it, it's the same adjustment in theory as a "macro" setting.

It's critical on one of these:



It's the silver knob peeking out from behind the handle just above where the focus assist plugs in.

Like you surmised it just might not be as acute on a shorter lens.
Link Posted: 9/20/2009 1:37:26 AM EST
Originally Posted By ColonelHurtz:
Originally Posted By steenkybastage:
Originally Posted By ColonelHurtz:

Remember this. For people, always focus on the eyeball.
Zoom in if you have to for critical focus, then zoom out to frame.


Just make sure your lens(es) actually keep their focus when zooming. I am pretty sure that most Canon lenses do not do this.

On lenses for broadcast video cameras you have a backfocus adjustment (IIRC, that's what it was called...) that you can adjust to keep your focal plan the same when you zoom... but I've never seen an SLR camera lens that has this option.

Then again, if you're zooming out (especially with small aperture and/or wideangle lens), it probably won't make a big difference.


That's not what back focus is for.
It adjust's the rear elements relationship to the film/sensor plane.
This changes from lens to lens or when you re-mount the same lens.

The symptom is loss of focus as you zoom out when it's not adjusted correctly but it's purpose is to adjust and fix the distance in the optical train.
I'm not sure why interchangeable still camera lenses don't have it, it's the same adjustment in theory as a "macro" setting.

It's critical on one of these:

http://i182.photobucket.com/albums/x298/hurtzc/CIMG0221.jpg

It's the silver knob peeking out from behind the handle just above where the focus assist plugs in.

Like you surmised it just might not be as acute on a shorter lens.


Well, now I know what the backfocus is supposed to do... I'll still use it to fix the zoom/focus problems on our cameras... even if it's just a side effect.

Ours aren't nearly as bulky as those... I wish their image circle was large enough to put on a FF DSLR, just to see what results I could get.

Link Posted: 9/20/2009 11:30:19 AM EST
[Last Edit: 9/20/2009 11:34:56 AM EST by ColonelHurtz]
You obviously know what it's for.

What I'm getting at is that it's intended to correct geometry.
The elements of the lens train that actually move when you zoom and focus will never achieve critical focus through their established range
if the back focus is not correct.

Focus is not absolute, save on a theoretical plane.
What they the brain interprets as acceptably focused is a range of depth in both directions from this plane.
See: circle of confusion
The back focus adjustment ensures that the optimal focal point of this range falls on and within the sensor plane.
Link Posted: 9/21/2009 4:26:37 AM EST
I had a lot of focus problems when I first started shooting.
Rather than use the AF points in auto-mode I set a single AF point in the center of the view finder and put that right on the focal point of my shots. it made a difference.
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